Why is CO (carbon monoxide) monodentate?

Moderators: Chem_Mod, Chem_Admin

vuongnaomi1L
Posts: 97
Joined: Wed Sep 30, 2020 9:56 pm

Why is CO (carbon monoxide) monodentate?

Postby vuongnaomi1L » Sat Dec 12, 2020 12:07 am

So the lewis structure of CO is C and O having triple bonds and there are 1 lone pair on each C and O. Since there are two lone pairs on the CO molecule, why isnt it a bidentate ligand?

Gabby Magat 3F
Posts: 103
Joined: Wed Sep 30, 2020 10:04 pm

Re: Why is CO (carbon monoxide) monodentate?

Postby Gabby Magat 3F » Sat Dec 12, 2020 12:22 am

Hi! I'm not too sure since I'm just starting to understand chelating complexes/polydentate ligands, but even though both atoms in carbon monoxide have a lone pair, you can't physically get both to bond to the central metal atom in a complex. You'd essentially be trying to "bend" the triple bond in between them, which wouldn't work.

So for polydentate ligands, you'd be looking for geometry where the lone pairs in the molecule are separated by a "spacer" (some atom without a lone pair itself. Because you can't bend/curve bonds between atoms, you need these spacers to form a ring-like shape so that the lone pairs are separated and both can bond to the same metal atom. I hope this made sense!

FrancescaHawkins2H
Posts: 80
Joined: Wed Sep 30, 2020 10:06 pm

Re: Why is CO (carbon monoxide) monodentate?

Postby FrancescaHawkins2H » Sat Dec 12, 2020 12:23 am

In my understanding, CO is a monodentate ligand because when one of the lone pairs becomes a bonding pair, it repels the other lone pair, which becomes too far away to create a second bond.

vuongnaomi1L
Posts: 97
Joined: Wed Sep 30, 2020 9:56 pm

Re: Why is CO (carbon monoxide) monodentate?

Postby vuongnaomi1L » Sat Dec 12, 2020 12:34 am

FrancescaHawkins3J wrote:In my understanding, CO is a monodentate ligand because when one of the lone pairs becomes a bonding pair, it repels the other lone pair, which becomes too far away to create a second bond.


This makes perfect sense! Thank you!

rhettfarmer-3H
Posts: 96
Joined: Wed Sep 30, 2020 9:59 pm

Re: Why is CO (carbon monoxide) monodentate?

Postby rhettfarmer-3H » Tue Dec 15, 2020 9:55 pm

CO is monodentate for many reasons to begin with the structure of CO-. Its one lone pair on C with a triple bond and a lone pair on O. Therefore, the O is negatively charged. Hence, since the structure is only 2 molecules long there are not enough spacers. Usually, you need 2 spacers because it wouldn't make sense for it to hit both ends if one side is bonded. Another reason is the minus charge is very EN so its going to hit the end mostly. to to note.

Astha Patel 2J
Posts: 96
Joined: Wed Sep 30, 2020 10:03 pm
Been upvoted: 2 times

Re: Why is CO (carbon monoxide) monodentate?

Postby Astha Patel 2J » Tue Dec 15, 2020 10:01 pm

The structure doesn't have spacers making it impossible for two lone pairs to become bonding pairs simultaneously. It would try and bend the bond.

Nancy Yao
Posts: 62
Joined: Wed Sep 30, 2020 9:38 pm

Re: Why is CO (carbon monoxide) monodentate?

Postby Nancy Yao » Wed Dec 16, 2020 5:46 am

H2O also has two lone pairs but it is a monodentate as well. I read some explanations online and they say that it is because water only has one donor atom and in polydentates there are more than one donor atoms. The other lone pair on the same atom cannot bond to the metal due to geometrical reasons.


Return to “Shape, Structure, Coordination Number, Ligands”

Who is online

Users browsing this forum: No registered users and 3 guests